Meltwater forms on top of the Greenland ice sheet in the summer. Some of it might percolate down to recharge subglacial lakes. Photo: NASA’s Goddard Space Flight Center/Maria-José Viñas

For decades, scientists working in Antarctica have been documenting subglacial lakes, bodies of water buried miles beneath the ice. They’ve spotted more than 400 of them, and even drilled into a few and found evidence for both living and long-dead lifeforms. But despite their ubiquity at the bottom of the world, no one had really looked to see if subglacial lakes were widespread beneath the Greenland ice sheet as well. Until now.

Only four subglacial lakes had previously been documented in Greenland. This week, an impressive survey published in Nature Communications added another 56 new lake candidates. And the researchers behind that survey think this is just the beginning. As in Antarctica, subglacial lakes could be a key feature of Greenland’s underbelly. Some of them might even influence the motion of the ice above as they fill and drain.

“I’m sure this is the tip of the iceberg in terms of what can be found,” co-author Stephen Livingstone, a glaciologist at the University of Sheffield, told Earther.

You’d see no obvious signs of them if you were walking across the ice, but there are a few ways researchers can detect subglacial lakes. In Antarctica, many have been spotted using satellites like NASA’s ICESat (and its recently launched replacement, ICESat-2), which flew over the same parts of the ice repeatedly to measure small changes in the height of the surface—interpreted to be the result of subterranean lakes filling and draining.

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Where lakes are less active, so to speak, scientists have other means of detecting them. They can, for instance, shoot radio waves through the ice and use their reflections to produce a picture of the bedrock below. That’s how, in the mid 1990s, researchers were able to confirm the presence of Lake Vostok, a 4,000-square-mile subglacial lake buried near the South Pole.

It’s that latter approach that helped scientists detect most of the new—albeit far smaller—subglacial lakes in Greenland. The authors turned to the vast database of radio echo sounding (RES) data collected by Operation IceBridge, a NASA-led airborne survey of Earth’s polar regions, from 1993 to 2016. From this, they spotted 54 subglacial lake candidates, or regions where the waves bouncing back produced a “brighter” signal indicative of pooled water at the ice sheet’s base. Eleven of those lakes could be observed over at least a decade of RSE data, boosting the researchers’ confidence that lakes are persistent.

Two more active-looking lakes were spotted by examining high-resolution topographic maps of Greenland’s icy surface. Taken together, these 56 lake candidates range in length from 0.2 to 5.9 km (0.1 to 3.7 miles). With the exception of the two active lakes in the southwest, most fell into three distinctive clusters in central-eastern, northern, and northwestern Greenland.

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Those in central-eastern Greenland tended to coincide with geothermal hotspots, suggesting that heat from Earth’s interior has played a role in their formation. The small number of active lakes scientists have documented, meanwhile, occur closer to the ice sheet’s margin, where there’s significant surface melt occurring in the summertime, suggesting they may be getting recharged as meltwater percolates from the surface down to bedrock.

That raises questions about whether climate change, which is accelerating melting across Greenland’s surface, could influence the activity of some of these lakes and in turn, the motion of the ice above them. Livingstone said it’s too early to say, but that understanding the connection between the lakes and motion of the ice above them is an important area for future research.

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There’s also plenty more work to be done simply documenting the existence of these lakes. Livingstone noted that while the data from Operation IceBridge is extensive, it still only covered a “small percentage” of Greenland’s ice sheet. He suspects many more lakes can be found looking more closely at those topographic maps, something the researchers are continuing to do.

Finally, scientists can now begin to do more detailed studies of individual lakes that have been found. Perhaps, in a few years, they’ll be gearing up to drill into one, as a team recently did in Antarctica. Who knows what they could discover in its waters.